1. Field of the Invention
The present invention relates to apparatus for detecting the presence of a transparent tubular article such as a test tube.
2. Description of the Prior Art
In automatic blood sample analysis systems, a test tube containing a blood sample that has been treated with radioisotopes is lowered into a nuclear detector that measures the radiation level. The test tube is handled by machine, to minimize the human exposure to radiation. Some indication must be provided to the system that a test tube has been lowered into place and that nuclear radiation detection should begin. An object of the present invention is to provide such an indicator.
Mechanical or electrical detectors are to be avoided as they may interfere with the isotope analysis. Magnetic detection cannot be used as the test tubes are non-ferrous. Optical detection is preferred, but is complicated because test tubes usually are made of highly transparent glass. Thus a beam of light sent directly through the test tube will not be attenuated sufficiently to permit reliable detection. Another object of the present invention is to provide an optical detector capable of sensing the presence of a highly transparent tubular article.